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When a click beetle is upside down on its back, it jumps upward by suddenly arching its back, transferring energy stored in a muscle to mechanical energy. This launching mechanism produces an audible click, giving the beetle its name. Videotape of a certain click-beetle jump shows that a beetle of mass \(m=4.0 \times 10^{-6} \mathrm{~kg}\) moved directly upward by \(0.77 \mathrm{~mm}\) during the launch and then to a maximum height of \(h=0.30 \mathrm{~m}\). During the launch, what are the average magnitudes of (a) the external force on the beetle's back from the floor and (b) the acceleration of the beetle in terms of \(g\) ?

Short Answer

Expert verified
(a) 0.015318 N (b) 389.77g

Step by step solution

01

Understand the Problem

We need to find two things: (a) the average magnitude of the external force acting on the beetle's back during launch, and (b) the acceleration of the beetle in terms of gravity, \(g\). The beetle has a mass of \(m = 4.0 \times 10^{-6} \text{ kg}\) and achieves a maximum height of \(0.30 \text{ m}\) after an initial upward movement of \(0.77 \text{ mm}\) during the launch.
02

Convert Units

Before using the given distances, convert \(0.77 \text{ mm}\) into meters: \(0.77 \text{ mm} = 0.00077 \text{ m}\). This makes all distances in meters, which is the standard unit for calculations in physics.
03

Calculate Initial Velocity After Launch

Using energy conservation, calculate the initial velocity \(v_0\) when the beetle leaves the floor. At maximum height, all kinetic energy is converted to potential energy: \(\frac{1}{2} m v_0^2 = mgh\). Rearranging gives \(v_0 = \sqrt{2gh}\). Use \(g = 9.8 \text{ m/s}^2\) and \(h = 0.30 \text{ m}\) to find \(v_0\).
04

Apply the Initial Velocity Formula

Calculate \(v_0 = \sqrt{2 \times 9.8 \times 0.30}\), which gives us \(v_0 \approx 2.42 \text{ m/s}\). This is the velocity just after the launch from the floor.
05

Use Kinematics to Find Acceleration

Use the kinematic equation \(v^2 = u^2 + 2as\) to find acceleration \(a\) during the launch phase, where \(v = v_0 = 2.42 \text{ m/s}\), \(u = 0\), and \(s = 0.00077 \text{ m}\). Rearranging gives \(a = \frac{v^2}{2s}\).
06

Calculate Acceleration

Substitute \(v = 2.42\) and \(s = 0.00077\) into \(a = \frac{v^2}{2s}\), yielding \(a \approx 3819.74 \text{ m/s}^2\). Express this as a multiple of \(g\): \(a \approx \frac{3819.74}{9.8} \approx 389.77g\).
07

Calculate the Average Force

The average force \(F\) can be calculated using \(F = ma\). With \(m = 4.0 \times 10^{-6} \text{ kg}\) and \(a = 3819.74 \text{ m/s}^2\), \(F = 4.0 \times 10^{-6} \times 3819.74 = 0.015279 \text{ N}\).
08

Account for Gravitational Force

The actual average external force exerted on the beetle's back is the calculated force plus the weight of the beetle because it has to overcome gravitational force as well: \(F_{external} = 0.015279 + mg\). Calculate \(mg = 4.0 \times 10^{-6} \times 9.8\), add this to get \(F_{external} \approx 0.015318 \text{ N}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Kinematics
Kinematics is a fundamental concept in physics that deals with the motion of objects without considering the forces that cause this motion. It involves quantities like distance, speed, velocity, and acceleration. By examining the motion of a click beetle, we can break down its path and calculate its motion properties. In our problem, the beetle starts from rest and moves a short vertical distance of 0.77 mm before reaching its maximum height of 0.30 m.

To analyze this, we convert all measurements into consistent units, such as meters for distances. The kinematics of the beetle's jump involves calculating its initial velocity just as it takes off. This is essential for further analysis using energy conservation and force calculation principles.
  • Distance covered during launch: converted to meters.
  • Initial velocity was determined from kinematics and energy relations.
Energy Conservation
Energy conservation is a crucial principle in physics that states that energy cannot be created or destroyed, only transferred or transformed. In this scenario, we examine how the click beetle uses this principle in its jump. The beetle stores energy as potential energy during the upward phase of its jump and converts muscle energy to mechanical energy, which propels it.

To find the initial velocity when the beetle leaves the ground, we use the fact that all the kinetic energy it has at takeoff (initially stored as muscle energy) transforms into gravitational potential energy at the peak of its jump:
  • Potential Energy (PE) at maximum height: \( mgh \)
  • Kinetic Energy (KE) at launch: \( \frac{1}{2} mv_0^2 \)
Rearranging these gives us an equation to calculate the initial velocity \( v_0 = \sqrt{2gh} \), which can then be used in further calculations.
Force Calculation
Force calculation is a key part of understanding how objects interact with each other. When the click beetle jumps, it experiences an external force from the floor that launches it into the air. The force calculation involves using Newton's second law, which states that force \( F \) is the product of mass \( m \) and acceleration \( a \).

For our beetle, we calculate the average force exerted by the floor during the launch:
  • Use the formula: \( F = ma \)
  • Include gravitational force: external force is \( F_{external} = F + mg \)
This accounts for the force needed to overcome gravity and provide the beetle with enough upward motion. By solving this, we understand both the beetle's interaction with the ground and its jump dynamics.
Acceleration
Acceleration is the rate at which an object's velocity changes with time. For the click beetle's launch, it experiences a rapid change in velocity over a very short distance of 0.77 mm. Using kinematic equations, we can determine this acceleration.

Apply the equation: \( v^2 = u^2 + 2as \), where:
  • \( v \) is the final velocity after launch, calculated as \( 2.42 \text{ m/s} \).
  • \( u \) is the initial velocity, which is 0.
  • \( s \) is the distance of launch.
The rearranged equation \( a = \frac{v^2}{2s} \) gives the beetle's acceleration. Expressing this acceleration in terms of \( g \) (standard gravity), reveals just how quick and powerful the beetle's jump is compared to normal gravitational forces on Earth.

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